Despite overwhelmingly vaccinated player populations, COVID-19’s second winter has decimated North American sports leagues at a level not seen since the industry reopened in 2020.

Every active league is seeing its regular season – and, in the case of the NFL, playoff push – jeopardized by the pandemic, from the NFL reporting a single-day high in cases to the NHL’s Calgary Flames being forced to postpone three games and the Chicago Bulls being forced to postpone two games after 10 players entered COVID-19 protocols.

Tuesday marked the one-year anniversary of a New York critical-care nurse becoming one of the first Americans to receive the COVID-19 vaccine, and in the year since, sports leagues have rewritten safety protocols and urged their players to get vaccinated once it became widely available last spring.

Despite high-profile holdouts such as Brooklyn Nets guard Kyrie Irving and Detroit Red Wings forward Tyler Bertuzzi, the effort was largely successful as the season began: the NFL reports nearly 95 percent of its players vaccinated, the NHL has just one unvaccinated holdout, and the NBA also exceeds 97 percent.

However, the last week has resulted in more postponements and protocol players than even navigating an unvaccinated 2020-21 winter.

According to the NFL Network, Monday was the NFL’s highest day of positive COVID-19 tests in the pandemic’s two seasons, with 36 players and one staffer forced into protocols.

According to Will Humble, director of the Arizona Public Health Association, the rash of breakthrough cases is most likely due to waning immunity among vaccinated players – particularly NBA players who may have been fully immunized as early as March or April. This is becoming more likely for those who received the ineffective Johnson & Johnson vaccine, which was popular among athletes due to its one-shot regimen.

And waning immunity necessitates a straightforward solution: booster shots.

A study conducted by a group of Veterans Affairs and public health officials found that from February 2021 to October 2021, vaccine antibodies fell from 88 percent to 48 percent, with the Johnson & Johnson vaccine having the steepest decline – which peaked at 13 percent at the eight-month mark. Fortunately, T cells’ performance in providing protection against potentially harmful health outcomes remains strong, according to Humble.

Following the outbreak on Monday, the NFL required booster shots for all tier 1 and 2 employees who work closely with players, including coaches who had previously agreed to a vaccine mandate.

The league cannot compel players to get vaccines, but it can strongly encourage them to get booster shots. However, with league testing frequency increasing as community spread of the highly contagious omicron variant increases, the likelihood of asymptomatic players testing positive is far greater.

And, with the majority of NFL teams in playoff contention – followed by a month of playoffs culminating in the Feb. 13 Super Bowl – the ramifications of a string of positives will only grow.

While the booster shot is not a silver bullet, both peer-reviewed and anecdotal evidence suggests it will be an important weapon in maintaining immunity.

Meanwhile, the newly discovered omicron variant poses yet another potential problem for frequently tested athletes.

While only one person in the sports league environment – a Washington Football Team staffer – tested positive for omicron, it has the potential to decimate a roster despite being less harmful to one’s health than the delta variant.

Humble, while emphasizing that data is still emerging, claims that omicron is far more contagious than delta, particularly among those who are unimmunized and have previously been infected with COVID-19. However, it has not been shown to evade immunity through vaccination any more than previous variants. A preliminary study published Tuesday in South Africa – where the variant was discovered – found it to be less virulent, but more contagious, than the delta variant.

The contagious aspect is less encouraging for immunized athletes, who are tested more frequently even when asymptomatic. In the NBA, for example, a positive test necessitates a 10-day isolation period or consecutive negative tests at least 24 hours apart, followed by a health screening.

Even if they are asymptomatic, these detours can derail a season. As a result, the booster could be the 2022 MVP in several leagues.