This I interesting, a proposal that Covid-19 is not the only causal agent kicking in the pandemic infections, but is the result of the combination of Covid-19 and XMRVs (human gamma retroviruses). This is the position of molecular biologist Judy Mikovits.
https://articles.mercola.com/sites/articles/archive/2020/05/03/is-the-new-coronavirus-created-in-a-lab.aspx?cid_source=dnl&cid_medium=email&cid_content=art1HL&cid=20200503Z1&et_cid=DM527830&et_rid=863832022
“One of the most shocking revelations Mikovits reveals is that she doesn’t believe SARS-CoV-2 is the cause of COVID-19 but merely serves to activate or wake up a dormant XMRV infection. To support her assertion, she states that COVID-19 patients have the same cytokine signature as the gammaretrovirus XMRV, which she published many years ago. XMRV stands for “xenotropic murine leukemia virus-related virus.” Xenotrophic refers to viruses that only replicate in cells other than those of the host species. So, XMRVs are viruses that infect human cells yet are not human viruses.2 The XMRV retrovirus is actually the virus that has the same cytokine storm signature as COVID-19, not coronaviruses, which are far more benign. (I delve into what retroviruses are in another section further below.) Additionally, there may be other infections that also are contributing to the infection, such as Borelia and Babesia or parasites, which may be why some of the antiparasite drugs like Ivermectin and hydroxychloroquine are working. Getting back to the issue of gammaretroviruses, Mikovits research showed that many of our vaccines are contaminated with them. How did this happen? In short, vaccine viruses were replicated and grown in animal cell cultures that were already contaminated with retroviruses. In other words, the root of the problem stems from the use of contaminated cell culture lines. Vaccine manufacturing frequently involves the use of animal tissues and many vaccines are grown animal culture cell lines. As noted in the 2010 paper, “Of Mice and Men: On the Origin of XMRV,” published in Frontiers in Microbiology (which Mikovits did not work on):3