While early last year’s most major challenge was coming to grips with a novel pandemic, now that scientists have developed multiple working, safe vaccines in an unprecedentedly short time, this year’s biggest challenge is managing inoculation on a global scale. For many people, 2021 is already a much better year (it’s not like you need a lot) just by virtue of the existence of these vaccines, for it signals the prospect of life returning back to normal — a life without daily Zoom meetings, physical distancing, and masks.

Here’s the thing though: even if you get vaccinated, don’t throw your face masks away just yet. In fact, we must all continue our strict regimen of rigorous hand washing, maintain social distancing, and keep the masks on the face when in public. That’s because the danger to one’s self, and especially those around us, doesn’t end with a vaccine. Here’s why.

Vaccination doesn’t offer immediate protection. The body needs weeks to properly respond

Both the Pfizer/BioNTech and Moderna vaccines require two doses spaced roughly four weeks apart to achieve the efficacy (the benefit that a vaccine provides compared to a placebo) recorded in clinical trials, which was nearly 95% for both. In a recent statement, Pfizer said that there is “no data” to suggest that a single dose of its coronavirus vaccine will provide protection from infection after 21 days.

That’s not to say that a single dose doesn’t offer any protection at all, it’s just that scientists don’t know exactly what the immune response for a single dose is. What’s more, the full potential of these mRNA vaccines is reached at least two weeks after receiving the second dose. All that’s to say that you’re vulnerable to infection weeks after receiving your first dose of the vaccine.

You might still be contagious

The clinical trials that established the safety and efficacy of the two mRNA vaccines only established whether or not participants became sick with COVID-19. But one of this pandemic’s buzzwords has been ‘asymptomatic’, meaning lacking symptoms. A vaccine may protect a person from falling sick with COVID-19, but there’s no way of telling 100% for sure that the same person can’t also become infected and perhaps transmit the virus to others like COVID-19 asymptomatic cases do.

This is not as absurd as it may sound. The vaccines are meant to be injected into the muscles, from where they start priming the body to produce antibodies against SARS-CoV-2. However, as is the case for most respiratory infections, this coronavirus most readily infects the body through the nose. The vaccine may produce enough antibodies to prevent sickness, but enough antibodies in the nose to prevent potentially contagious viral load.

“If you protect against clinical disease, that’s very good,” Dr. Anthony Fauci said in the interview with the “Today” show. “But if you also even prevent a person from getting actually infected, that would mean that you’re preventing someone from passing the infection on to someone else, and that kind of interferes with the chain of transmission.”

There are reasons to be optimistic, though. A study on people who received an intramuscular flu vaccine found abundant antibodies in the nose, and things may be not much different for a COVID vaccine. A nasal vaccine would dispel such worries.

Subsequent trials this year will answer many such unknowns, but in the meantime, we should still wear a mask just to be safe.

We don’t know how long immunity lasts

Because these vaccines have been developed with truly unprecedented speed — they’ve come about 10 times faster to the market than your typical vaccine — there are still many properties that are uncertain. One important metric that will heavily influence mass vaccination campaigns in the future is the length of immunity, which so far is unknown. The good news is that it likely lasts for at least six months, which is roughly the time since the first vaccines were administered in clinical trials.

No vaccine is 100% effective: There will always be some uncertainty because the real world is not a clinical trial

There can be important differences in terms of outcome between clinical trials and real-world mass vaccinations. Unexpected things can happen in terms of how the vaccine is stored, transported, and administered, as well as a result of each individual’s biology. The much-heralded 95% efficacy we’ve all heard about may differ significantly in the real world. For instance, the vaccine may indeed prevent 95% of cases of severe illness — which is a huge success in and of itself — but the efficacy of prevention of mild disease could be much lower than that. Mild disease won’t threaten your life but may make you contagious. Then there’s still that 5% that will require protection (i.e. social distancing and face masks) as long as outbreaks are still ongoing in a community.

Face masks are still mandatory in public in many countries (and herd immunity threshold is unknown)

As the second wave of the pandemic is sweeping through the UK, fueled by a new, more potent variant with a higher transmission rate that may have already spread to the rest of the world, restrictions are likely to get tougher before they get lighter. In many places, masks are mandatory in the public, both indoors and outdoors. Until the vast majority of the population is vaccinated to build up herd immunity, these restrictions will likely stay in place. A vaccine certificate could exempt you from wearing a mask, depending on how your local government chooses to handle this issue, but that seems rather unlikely at this stage.

The only safe time not to wear a mask anymore is when this pandemic is over. When will that be? No one knows. The name of the game of 2020 was social distancing. That’s still as true as ever for 2021, with the added caveat that we’re now also eyeing herd immunity. Some experts believe herd immunity will be reached when about 70% of the population is inoculated against the virus, but the reality no one knows for sure. For measles, 95% of the population needs to be vaccinated to achieve herd immunity.

Considering 37% of Americans said they would not agree to take the vaccine, herd immunity could be thwarted in the future. In the early stages of vaccination, this is not a problem, but as coverage increases, much about how this pandemic evolves will hinge on the public recognizing the major role they have to play.

So, be prepared to continue wearing masks for the foreseeable future, probably for the rest of 2021 until a large enough number of the general public is vaccinated, leaving this pesky virus with no more hosts left to cause devastating outbreaks.

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This article is part of a series by the ZME Science editorial staff meant to inform and educate the public concerning the coronavirus vaccines. This is not medical advice. You should consult your doctor before making a health decision based on information you read online.