Your guide to every COVID-19 vaccine question
How do you know if the available COVID-19 vaccines are safe? How will they protect against existing and future variants? Can you mix doses?
Below are the most frequently asked questions about the COVID-19 vaccine:
Are some COVID-19 vaccines more effective than others?
It’s hard to tell since they weren’t directly compared in studies. But experts say the vaccines are alike on what matters most: preventing hospitalizations and deaths.
“Luckily, all these vaccines look like they’re protecting us from severe disease,” said Dr. Monica Gandhi of the University of California, San Francisco, citing study results for five vaccines used around the world and a sixth that’s still in review.
And real-world evidence as millions of people receive the vaccines show they're all working very well.
Still, people might wonder if one is better than another since studies conducted before the vaccines were rolled out found varying levels of effectiveness. The problem is they don't offer apples-to-apples comparisons.
Consider the two-dose vaccines from Pfizer and Moderna, found to be about 95% effective at preventing illness. Studies for those shots counted a COVID-19 case whether it was mild, moderate or severe — and were conducted before worrisome mutated versions of the virus began circulating.
Then Johnson & Johnson tested a single-dose vaccine and didn't count mild illnesses. J&J’s shot was 66% protective against moderate to severe illness in a large international study. In just the U.S., where there's less spread of variants, it was 72% effective. More importantly, once the vaccine’s effect kicked in it prevented hospitalization and death.
AstraZeneca's two-dose vaccine used in many countries has faced questions about the exact degree of its effectiveness indicated by studies. But experts agree those shots, too, protect against the worst outcomes.
Around the world, hospitalizations are dropping in countries where vaccines have been rolling out including Israel, England and Scotland — regardless of which shots are given. And the U.S. government’s first look at real-world data among essential workers provided further evidence that the Pfizer and Moderna vaccines are highly protective -- 90% -- against infections whether there were symptoms or not.
Can I still spread the coronavirus after I’m vaccinated?
It’s possible. Experts say the risk is low, but are still studying how well the shots blunt the spread of the virus.
The current vaccines are highly effective at preventing people from getting seriously sick with COVID-19.
But even if vaccinated people don’t get sick, they might still get infected without showing any symptoms. Experts think the vaccine would also curb the chances of those people spreading the virus.
“A vaccinated person controls the virus better, so the chances of transmitting will be greatly reduced,” said Dr. Robert Gallo a virus expert at the University of Maryland School of Medicine.
Among the evidence so far: Studies suggesting if people do get infected despite vaccination, they harbor less coronavirus in the nose than the unvaccinated. That makes it harder to spread.
Trying to settle the question, the U.S. is starting a study of college students willing to undergo daily nasal swab testing.
Given the uncertainty and the arrival of more contagious variants, experts say fully vaccinated people should continue to wear masks and social distance in public and when visiting with unvaccinated people at high risk for severe illness if infected.
“We still have to be cautious,” Gallo said. “The vaccine is essential. But it is not a cure-all that ends the epidemic tomorrow.”
Other factors can also affect the likelihood of a vaccinated person spreading the virus, including vaccination rates in the community and whether there’s an ongoing surge in cases locally.
“We want to think it’s all or none, but it’s very situation-specific,” said Dr. Laraine Lynn Washer, an infectious disease expert at the University of Michigan.
I got the COVID-19 vaccine. What can I safely do?
You can enjoy small gatherings again, but should continue wearing a mask and social distancing in public.
The U.S. Centers for Disease Control and Prevention says fully vaccinated people can gather maskless with other vaccinated people indoors. It also says you can meet with unvaccinated people from one household at a time, if those people are considered at low risk of severe COVID-19.
In public, the CDC recommends that vaccinated people continue wearing masks, avoid large gatherings and stay apart from others.
A person is considered fully vaccinated two weeks after receiving the last required dose of vaccine.
Guidance on other activities for vaccinated people remains cautious. The CDC expects to update the guidance to allow more activities as infections decline and vaccinations increase.
One reason to keep your guard up after getting one dose of a two-dose vaccine: infection while having partial protection sets up the potential for the virus to mutate, said Dr. Joshua LaBaer, director of the Arizona State University’s Biodesign Institute.
When will children be able to get COVID-19 vaccines?
It depends on the child's age, but some teenagers could be rolling up their sleeves before too long.
The Pfizer vaccine already is cleared for use starting at age 16. That means some high schoolers could get in line for those shots whenever they become eligible in their area, either because of a medical condition or once availability opens up.
Pfizer and Moderna both have completed enrollment for studies of children ages 12 and older, and expect to release the data over the summer. If regulators clear the results, younger teens likewise could start getting vaccinated once supply allows. The Moderna vaccine is currently cleared for people 18 and older.
Researchers started with older children because they tend to respond to vaccines most similarly to adults. Testing even younger groups is more complex, because they may require a different dose or have differing responses.
“Children are not just small adults,” said pediatrician Dr. James Campbell of the University of Maryland School of Medicine. “The younger you get, the higher the odds are that things could be different.”
Children develop serious illness or die from COVID-19 at much lower rates than adults, but can still spread the virus.
“There’s no question: we do want to immunize children,” said Drexel University pediatrics professor Dr. Sarah Long.
Pfizer and Moderna expect to start studies in children 11 and younger later this year.
“It’s unlikely we could get community protection without immunizing children,” Long added. “This is the lynchpin to getting everything back to some kind of normalcy.”
How are COVID-19 vaccine makers going to adapt to variants?
By tweaking their vaccines, a process that should be easier than coming up with the original shots.
Viruses constantly mutate as they spread, and most changes aren't significant. First-generation COVID-19 vaccines appear to be working against today's variants, but makers already are taking steps to update their recipes if health authorities decide that's needed.
COVID-19 vaccines by Pfizer and Moderna are made with new technology that's easy to update. The so-called mRNA vaccines use a piece of genetic code for the spike protein that coats the coronavirus, so your immune system can learn to recognize and fight the real thing.
If a variant with a mutated spike protein crops up that the original vaccine can't recognize, companies would swap out that piece of genetic code for a better match — if and when regulators decide that's necessary.
Updating other COVID-19 vaccines could be more complex. The AstraZeneca vaccine, for example, uses a harmless version of a cold virus to carry that spike protein gene into the body. An update would require growing cold viruses with the updated spike gene.
The Food and Drug Administration said studies of updated COVID-19 vaccines won’t have to be as large or long as for the first generation of shots. Instead, a few hundred volunteers could receive experimental doses of a revamped vaccine and have their blood checked for signs it revved up the immune system as well as the original vaccines.
More difficult is deciding if the virus has morphed enough to modify shots.
Globally, health authorities will monitor coronavirus mutations to spot vaccine-resistant mutations. They'd also have to decide whether any revamped vaccine should protect against more than one variant.
Overall the process would be similar to what already happens with flu vaccine. Influenza viruses mutate much faster than coronaviruses, so flu shots are adjusted every year and must protect against multiple strains.
How do we know the COVID-19 vaccines are safe?
Scientists look for safety issues during the testing phase and continue their monitoring as shots roll out around the world. So far, the only serious warning to emerge is a rare risk of severe allergic reactions.
Different types of COVID-19 vaccines have been authorized and it’s possible side effects will differ for each — although there's more public data on the vaccines being rolled out in Western countries than elsewhere. Countries also vary in their vaccine standards, with some allowing the use of shots before final-stage testing involving large numbers of volunteers.
But in the U.S., Britain and European Union, regulators required any vaccine to be tested in tens of thousands of people before distribution. So far, the U.S. is using shots from Pfizer and Moderna, while Britain and Europe have cleared those plus the AstraZeneca vaccine.
Those companies’ large studies found that common side effects were minor and typical of the immune system revving up: soreness in the arm, fever and flu-like symptoms including fatigue, chills and headache.
But since extremely rare problems might not turn up even in large tests, the vaccines still are being monitored. The U.S. and British governments and the European Medicines Agency track reports filed by health workers and the public about suspected side effects. Extra scrutiny in the U.S. includes tracking insurance claims for red flags. And U.S. vaccine recipients can sign up for a program that sends text messages to see if they're feeling side effects.
Those checks are proving reassuring.
People are supposed to wait around for a short time after vaccination in case they have a severe allergic reaction, called anaphylaxis. Such incidents so far have been rare, with between 2 and 5 anaphylaxis reports for every million vaccine doses in the first weeks of U.S. inoculations, according to the Centers for Disease Control and Prevention.
Officials expected to receive reports of health problems, even deaths, that occur just by chance in the days or weeks after vaccination, given the huge numbers of people, including the frail elderly, getting inoculated.
Deaths and other serious events are investigated to see if the vaccine played a role. Authorities consider the person's overall health and how often the reported condition occurs without vaccination. With more than 52 million vaccine doses administered in the U.S. by mid-February, the CDC said it hasn't detected any patterns in deaths that signal a safety problem.
Should I take painkillers before or after a COVID-19 vaccine?
It's best to avoid painkillers before receiving the COVID-19 vaccine, unless you routinely take them for a medical condition. Although the evidence is limited, some painkillers might interfere with the very thing the vaccine is trying to do: generate a strong immune system response.
Vaccines work by tricking the body into thinking it has a virus and mounting a defense against it. That may cause arm soreness, fever, headache, muscle aches or other temporary symptoms of inflammation that can be part of that reaction.
“These symptoms mean your immune system is revving up and the vaccine is working,” Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, said in a recent news briefing.
Certain painkillers that target inflammation, including ibuprofen (Advil, Motrin and other brands) might curb the immune response. A study on mice in the Journal of Virology found these drugs might lower production of antibodies — helpful substances that block the virus from infecting cells.
If you're already taking one of those medications for a health condition, you should not stop before you get the vaccine — at least not without asking your doctor, said Jonathan Watanabe, a pharmacist at the University of California, Irvine.
People should not take a painkiller as a preventive measure before getting a vaccine unless a doctor has told them to, he said. The same goes for after a shot: “If you don’t need to take it, you shouldn’t,” Watanabe said.
If you do need one, acetaminophen (Tylenol) “is safer because it doesn’t alter your immune response,” he added.
, such as holding a cool, wet washcloth over the area of the shot and exercising that arm. For fever, drink lots of fluids and dress lightly.
Call your doctor if redness or tenderness in the arm increases after a day or if side effects don’t go away after a few days, the CDC says.
What should I know about COVID-19 vaccines if I’m pregnant?
Vaccination is likely the best way to prevent COVID-19 in pregnancy, when risks for severe illness and death from the virus are higher than usual.
The American College of Obstetricians and Gynecologists says COVID-19 vaccinations should not be withheld from pregnant women, and that women should discuss individual risks and benefits with their health care providers.
The U.S. government’s emergency authorization for the Pfizer and Moderna vaccines being rolled out for priority groups doesn’t list pregnancy as a reason to withhold the shots.
But the OB-GYN group says women should consult their doctors, since COVID-19 vaccines have not yet been tested in pregnant women. Evidence about safety and effectiveness is reassuring from studies that inadvertently included some women who didn't know they were pregnant when they enrolled.
More answers are expected from upcoming research, including a study by Pfizer and German partner BioNTech expected to start early this year that will include pregnant women.
Experts say there’s no reason to think the two authorized vaccines would harm fetuses. They might even protect them from developing COVID-19, although that hasn't yet been proven, said Dr. Denise Jamieson, chair of gynecology and obstetrics at Emory University School of Medicine.
That thinking comes in part from experience with vaccines for influenza and whooping cough, which are approved for use in pregnancy and protect newborns and their mothers from developing those diseases.
How quickly do I need a second COVID-19 vaccine shot?
The first COVID-19 vaccines in the U.S. require two doses a few weeks apart.
People should get some degree of protection within two weeks of the first shot, with the second shot bringing about the vaccine’s full protection. For the , the second shot is supposed to be after three weeks. For , it’s four weeks.
But how closely those guidelines should be followed has been a point of difference for the United States and the United Kingdom, which has been rolling out the Pfizer vaccine and one by Astrazeneca that requires two doses given four weeks apart.
To get more first shots into people and give them at least some degree of protection, the UK says it’s OK to delay the boosters for as long as 12 weeks. But that strategy has been nixed in the U.S., where regulators say there’s no science backing the approach.
A major concern is that it’s unknown how long the partial protection from one dose can last. “There is no data to demonstrate that protection after the first dose is sustained after 21 days,” Pfizer said.
U.S. regulators agreed, saying too few people in the Pfizer and Moderna vaccine studies missed their scheduled boosters to have enough data to show the strategy might work.
The timing of the shots doesn't have to be exact in the U.S., though; the Centers for Disease Control and Prevention says the second shots can be given up to four days earlier or later.
Will COVID-19 vaccines work on new coronavirus variants?
Although experts believe the vaccines approved to prevent COVID-19 will also work on new strains of the virus, they’re still working to confirm that.
A coronavirus variant in the United Kingdom has caused alarm because of the possibility that it might spread more easily. But even if that turns out to be true, experts say the COVID-19 vaccines being rolled out will likely still work on new variants.
Dr. Anthony Fauci, the top U.S. infectious disease expert, said data coming from Britain indicates the vaccines still will block the virus. But the U.S. also will do tests to be sure.
Viruses often undergo small changes as they reproduce and move through a population. In fact, the slight modifications are how scientists track the spread of a virus from one place to another.
But if a virus mutates significantly enough, one worry is that current vaccines might no longer offer as much protection. And although that's a possibility to watch for over time with the coronavirus, experts say they don't believe it will be the case with the variant in the U.K.
“My expectation is, this will not be a problem,” said Moncef Slaoui, the chief science adviser for the U.S. government’s COVID-19 vaccine push.
Can I stop wearing a mask after getting a COVID-19 vaccine?
No. For a couple of reasons, masks and social distancing will still be recommended for some time after people are vaccinated.
To start, the first coronavirus vaccines require two shots; Pfizer’s second dose comes three weeks after the first and Moderna’s comes after four weeks. And the effect of vaccinations generally aren't immediate.
People are expected to get some level of protection within a couple of weeks after the first shot. But full protection may not happen until a couple weeks after the second shot.
It's also not yet known whether the nation's approved vaccines protect people from infection entirely, or just from symptoms. That means vaccinated people might still be able to get infected and pass the virus on, although it would likely be at a much lower rate, said Deborah Fuller, a vaccine expert at the University of Washington.
And even once vaccine supplies start ramping up, getting hundreds of millions shots into people's arms is expected to take months.
Fuller also noted vaccine testing is just starting in children, who won’t be able to get shots until study data indicates they're safe and effective for them as well.
Moncef Slaoui, head of the U.S. vaccine development effort, has estimated the country could reach herd immunity as early as May, based on the effectiveness of the Pfizer and Moderna vaccines. That's assuming there are no problems meeting manufacturers' supply estimates, and enough people step forward to be vaccinated.
