For the years ended December 31, 2021 and 2020, the total comprehensive loss is as follows:

Major items causing the Company’s income tax rate to differ from the statutory rate of approximately 26.5% ( December 31, 2020 – 26.5%) are as follows:

The tax effects of temporary differences that give rise to significant portions of the unrecognized deferred tax assets are presented below:

The valuation allowance at December 31, 2021 was primarily related to net operating loss carryforwards that, in the judgment of management, are not more-likely than-not to be realized. In assessing the realizability of deferred tax assets, management considers whether it is more-likely than-not that all or some portion of the deferred assets will not be realized. This ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the period in which those deductible temporary difference become deductible. Based on the history of losses and projections for future taxable income, management believes that it is not more-likely than-not that the Company will realize the benefits of these deductible temporary differences (e.g. deferred tax assets).

The Company has Canadian undeducted research and development expenditures, totaling $19.0 million that can be carried forward indefinitely. The Company also has Canadian non‑refundable federal and provincial investment tax credits of approximately $3.3 million which are available to reduce future federal taxes payable and begin to expire in 2022, as well as non‑refundable US research and development tax credits of approximately $1.8 million which are available to reduce future US taxes payable and begin to expire in 2038.

In addition, the Company has Canadian non-capital loss carryforwards of $177.9 million. To the extent that the non-capital loss carryforwards are not used, they begin to expire in 2026. The Company also has US non-capital loss carryforward of $0.9 million, To the extent that the non-capital loss carryforwards are not used, they begin to expire in 2034.

The Company files income tax returns with Canada and its provinces and territories. Generally, we are subject to routine examinations by the Canada Revenue Agency ("CRA"). Income tax returns filed with various provincial jurisdictions are generally open to examination for periods of four to five years subsequent to the filing of the respective return.

The Company also files income tax returns for our U.S. operations and subsidiary with the U.S. federal and state tax jurisdictions. Generally, we are subject to routine examination by taxing authorities in the U.S. jurisdictions. There are presently no examination of our U.S. federal and U.S. state returns. We believe that our tax positions comply with the applicable tax law.